In the machining of metallic articles, inadequate chip disposal and machine chatter are two important factors that can limit productivity. The limitation on productivity becomes more serious when the machining is conducted at higher cutting speeds, higher removal rates and, when machining those materials that yield a segmental or shear-localized type of chip.
Short chips are always preferred over long, stringy chips, not only from the point of view of chip disposal, but also from the point of view of human safety and potential damage to the part being machined. One solution to the problem of chip disposal is the use of cutting inserts constructed with appropriate chip-groove geometry. Another way to handle the problem is by selecting the proper tool geometry, especially in respect to the back rake angle.
This invention presents still a further solution to the problem of chip disposal and, at the same time reduces chatter. The problem of chatter addressed by this invention is particularly evident in the machining of difficult-to-machine materials, such as the machining of titanium alloys. Other materials, such as nickel base superalloys (e.g. Inconel 718) and hardened alloy steels (e.g. AISI 4340), also present this problem depending upon the cutting speed and the feed. When such chatter is encountered, the frequency of oscillation varies proportionately with the cutting speed and inversely with the feed. The feed approximates the thickness of the uncut chip. Application of this invention provides a more uniform cutting force and a reduction in the amplitude of chatter.
The tool insert design of this invention is particularly applicable to such tool materials as cemented carbides such as straight WC and multi-carbides in a cobalt binder, TiC in a Ni-Mo binder and coated carbides and ceramic materials such as alumina, mixtures of alumina with TiO, ZrO.sub.2 and/or TiC, and mixtures of silicon nitride with TiC, Al.sub.2 O.sub.3, Y.sub.2 O.sub.3.
Certain definitions are useful for a better understanding of this invention:
Segmental chip - a continuous chip with a periodic, but asymmetric variation in chip thickness. PA1 Shear-localized chip - a continuous serrated chip in which during the upsetting stage intense shear occurs between the chip segment being formed and the chip segment immediately preceding. PA1 Chatter of the forced type - a vibration of the metal cutting machine induced by the cutting operation, when chips of either the segmental or shear-localized types are being produced.
More detailed description of the formation of segmental and shear-localized chips is set forth on page 122 of the article by Komanduri, et al., "On The Catastrophic Shear Instability in High-Speed Machining of An AISI 4340 Steel" [Journal of Engineering for Industry, May 1982, Vol. 104, pp. 121-131].